Characterisation of bacteria in soils under barley monoculture and crop rotation

Rhizobacterial populations on barley roots, originating from experimental f ields with barley monoculture (MC) and crop rotation (CR), were analyzed fo r their fatty profiles. In the first part of the study, the profiles of 118 8 isolates were statistically analyzed to identify clusters of bacteria wit h a possible high prevalence in MC or CR soil. One such cluster was found, termed Ps4-C4, with characteristically high contents of C12:1 3OH (9.8%) an d an unidentified fatty acid with the equivalent chain length (ECL) of 12.3 5, which was provisionally named ECL12.35 (4.5%). Bacteria in Ps4-C4 were a lso rich in C10:0 3OH (8.3%) and C12:0 3OH (8.1%). The cluster consisted of 109 isolates, 86 from MC populations and 23 from CR, none of which could b e identified by means of fatty acid analysis. In the second part of the stu dy, fatty acid profiles of 240 microbial populations from the same fields w ere analyzed. Results showed higher relative contents of C12:1 3OH, ECL12.3 5, C10:0 3OH and C12:0 3OH in MC populations, which also had a high proport ion of C12:0 2OH and C16:0. A detailed statistical analysis of the correlat ions between the fatty acids indicated that Ps4-C4 alone explained the high er portions of C12:1 3OH and ECL12.35 in populations from MC soil, while ot her bacterial groups are seem to have contributed to the elevated contents of C10:0 3OH and C12:0 3OH. Some common functional characteristics of bacte ria in the Ps4-C4 cluster are also described. (C) 2000 Elsevier Science Ltd . All rights reserved.